Could tracking dust storms over Africa help predict hurricanes in the U.S.? Amato Evan thinks so. The University of Wisconsin researcher and his team have connected the dry, windswept plains of the Sahara to the intensity of the Atlantic hurricane season.

The hurricanes that hit North America and the Caribbean are spawned in the warm surface waters of the Atlantic Ocean. Dust from North Africa--generated by storms blowing from east to west across the Sahara--flows across the West African coast and out over the North Atlantic, "robbing the ocean of the sunlight that helps it to maintain its temperature or to warm in the summer," Evan explains. Higher dust density over the Atlantic means cooler sea surface temperatures--and weaker storms.

To prove the connection, Evan and his colleagues combined a complex climate computer model with measurements gathered since 1979 by the U.S. National Oceanic and Atmospheric Administration's Polar Operational Environmental Satellites (POES). Traveling from pole to pole every few hours, these three satellites measure surface temperature, vegetation health and something called "cloud aerosol properties" (the word "aerosols" is science-speak for tiny particles suspended in the atmosphere).

The polar orbiters gave the researchers four to six glances a day at every spot on Earth, according to Andrew Heidinger, a NOAA scientist working with Evan. But how to interpret the data? "The big problem is separating dust from clouds," he says. "Amato came up with a method that turns out to be very stable and consistent over time."

Evan has created a tool for forecasting future dust levels based on the prior year's storms, which he used to forecast conditions for the 2008 Atlantic hurricane season. "Cooler sea surface temperatures generally are equated with lower hurricane activity," he says. "This spring we predicted that the cooling effect due to dust would be about average, in contrast to years like 2004 and 2005, when there was not as much dust, and therefore the cooling effect the dust has on ocean temperatures was much weaker," and sea surface temperatures were unusually warm.

Does this mean that 2008's storm season will be mild? In comparison with a year like 2005—the year of Katrina and Rita—the answer is a guarded "probably," since cooler sea surface temperatures inhibit the formation of powerful storms. But Evan's forecast doesn't rule out major hurricanes this season: an average amount of dust over the ocean may simply mean that dust won't tip the balance one way or another in relation to the other factors that help breed hurricanes. And Evan notes that the odds were good for getting a seasonal forecast right this year, since most years are average. "I'll feel more confident in my forecasts of dust storm activity," he says, "if I can correctly anticipate an above- or below-average season."

Evan is also working with the Tropical Meteorology Project at Colorado State University, which issues hurricane season forecasts. "One thing we can do is look at how much did it rain in Africa over the last 12 months," he says. "There's a little bit of a predictive element of how much dust there will be next year. If last year were wetter than normal, we'd expect less dust-storm activity."

Energy traders and people in the reinsurance industry--private sectors that have a lot of money exposed to business risks involving the weather--have inquired about his work, Evan says. But forecasting dust is a very new field. "It's going to take a while to understand just how important dust storms are to hurricanes," he says, and "how we can use that information to improve forecasts."